Charge Sensitive Vibrations and Electron-Molecular Vibration Coupling in Bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF)

Abstract

A complete analysis of the vibrational dynamics of the most important molecule in the field of organic superconductors, bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF), has been performed through first-principles calculations. Different ionization states have been investigated, both as isolated BEDT-TTF unit, and as symmetric self-dimer. The ionization process affects the frequencies of some vibrations, the "charge sensitive modes", but also their intensities. In particular, a 100-fold increase in the infrared intensity of the antisymmetric CdC stretching mode is predicted to occur upon removal of one electron. The discovery of this dramatic difference will help to interpret the spectral phenomena observed in correspondence to the charge-order processes undergone by some BEDT-TTF salts. The electronmolecular vibration (e-mv) coupling and its effects on the infrared spectra is also fully reanalysed by adopting the proper molecular symmetry of the BEDT-TTF + monomer, and by investigating (BEDT-TTF) 2 2+ and (BEDT-TTF) 2 + dimers. A new approach to estimate the relative values of the e-mv coupling constants is proposed.

How intermolecular geometrical disorder affects the molecular doping of donor–acceptor copolymers

“…Following a standard procedure described in the Methods section, we scaled the calculated frequencies by a factor o1 in the part of the spectra 41,280 cm À 1 (ref. 36). Figure 3a shows also the spectrum of Complex-1, a molecular cluster obtained by energetically optimizing the geometry of F4-TCNQ in proximity of one of the CPDT moieties of PCPDT-BT (Fig.…”

Giant infrared absorption bands of electrons and holes in conjugated molecules

“…With the low dielectric constant (e ¼ 4.89) of chloroform, it is plausible that there are few free ions, and that the ion pairs are tightly bound. Quantum-chemical calculations often give good predictions of IR spectra for small molecules, including ions of terphenyl 4 , and even for charge-transfer salts 41 . The calculations reproduce some features of the observed spectra fairly well.…”

Infrared and Raman Studies of Charge Ordering in Organic Conductors, BEDT-TTF Salts with Quarter-Filled Bands

“…A more recent estimation gives g 3 = 0.076 eV from the analysis of the infrared spectrum of κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]-Br 0.85 Cl 0.15 [55]. Using the same data, Girlando interpreted this as g 2 = 0.075 eV [56]. The estimation of the coupling constants of ν 2 and ν 3 from the infrared spectrum seems to be unfixed still now.…”